High-frequency electric discharge device



1946- R. J. BONDLEY HIGH FREQUENCY ELECTRIC DISCHARGE DEVICE Fild Nov. 1:5, 1942 Inventor- Ralph J. Bondleg,

by W

HIS Attorneg.

Patented Aug. 20, 1946 HIGH-FREQUENCY ELECTRIC DISCHARGE DEVICE Ralph J. Bondley, Scotia, N. Y., assignor to General Electric Company, a corporation of New York Application November 13, 1942, Serial No. 465,424

Claims.

My invention relates to high frequency electric discharge devices and more particularly to ultra high frequency magnetrons of the space resonant type.

In electric discharge devices of the magnetron type, it is of considerable importance to provide structure which permits the establishment of the desired electrostatic and magnetic fields of desired intensity and configuration, and it is also important that the supporting structure be capale of withstanding voltage gradients of appreciable magnitude to obtain a power output commensurate with the size of the equipment. Furthermore, it is of considerable consequence to position and arrange the elements and supporting structure therefor so that the operation of the discharge device does not cause the deposition of a layer of conductive material on the insulating parts, which would cause the discharge device to become inoperative after a short period of operation.

In accordance with the teachings of my inven tion described hereinafter, I provide new and improved-construction for an ultra high frequency magnetron which not only affords the desired insulating qualities of the structure but also minimizes heat transfer between elements thereof.

More particularly, I provide new and improved structure for an ultra high frequency magnetron of the type disclosed and broadly claimed in a copending patent application Serial No. 447,903 of Elmer D. McArthur, filed June 22, 1942, and which is assigned to the assignee of the present application.

It is an object of my invention to provide a new and improved ultra high frequency electric discharge device.

Zt is another object of my invention to provide a new and improved structure for supporting an electrode of an ultra high frequency magnetron of the space resonant type.

It is a further object of my invention to provide a new and improved cathode supporting structure for an ultra highfrequency magnetron wherein the associated insulating means is protected by preventing the deposition of a conductive layer material thereon incident to the evaporation of electrons from the electron emissive surface of the cathode.

Briefly stated, in the illustrated embodiment of my invention I provide a new and improved cathode supporting structure for an ultra high frequency magnetron which comprises a rigid concentric cable construction which extends through one of the associated magnetic pole pieces. The

inner conductor of the concentric cable extends through a cylindrical cathode and serves as a support for a shielding means, or member, which is positioned between the anode structure and the other associated pole piece. The insulating means which supports the rigid cable construction is displaced an appreciable distance from the end of the pole piece, thereby reducing the possibility of establishing any conductive layer thereon, and the outer conductor of the concentric cable is joined to the cylindrical cathode by means of a rigid metallic member which serves to shield the insulator. I also provide an improved structure for joining the cathode to the concentric cable whereby the heat transfer between the cable and the cathode is minimized.

For a better understanding of my invention, reference may be had to the following description taken in connection with the accompanying drawing, and its scope will be pointed out in the appended claims. Fig. 1 diagrammatically illustrates an embodiment of my invention as applied to an ultra high frequency magnetron of the space resonant type employing a pair of permanently magnetized pole pieces, and Fig. 2 is a plan view of the anode structure. Figs. 3 and 4 diagrammatically illustrate an alternative cathode supporting structure.

Referring now to Fig. 1 of thedrawing, I have there illustrated my invention as applied to an electric discharge device, such as an ultrahigh frequency magnetron, including an elongated cylindrical container, the lateral wall structure of which is provided by a single metallic tube I which rolled steel, or the like. The ends of the container or tube l are closed by flanged members 2 and 3 which are welded or otherwise hermtically joined to the inner surface of tube I. The outer surface of the envelope may be provided with a plurality of radially extending fins (not shown) for the purpose of dissipating heat.

Within the container and approximately at its central region there is provided an anode structure 4 shown in detailed plan view in Fig. 2. The anode structure 4 is preferably of circular configuration provided with an enlarged central opening 5 and a plurality or series of smaller openings 6 arranged symmetrically about the central opening. The central opening is joined to the openings ,6 by means of radially extending slots 1.

The anode structure 4, which preferably consists of copper, is supported by being brazed to the interior wall of tube I. To facilitate the brazing operation, small channels 8 are cut in the outer periphery of the structure and these are used to receive rings of brazing material ap-. plied before the anode structure is inserted With.- in the tube I. A relatively large circumferentially extending channel 9 serves to reduce the overall weight of the anode structure.

Within the opening of the anode structure there is provided a thermionic cathode such as an indirectly heated cathode comprising a metallic.

sleeve N3 of nickel or other suitable material, and I which is coated externally with a suitable acti- Y vating material such as barium oxide.

maintained at an emissive temperature.

Within the sleeve Ill, there is provided afilamentary cathodeheating element H bywhich the cathode is .tainer. '2! also serve as communicating paths for the same purpose. An evacuation or exhaust tubula- 'tion 26 maybe welded or otherwise sealed to the In operation of the device, a space charge is I assumed to be developed in the space defined between the cathode sleeve I8 and the surrounding anode structure by the application of a suitable potential impressed .therebetween. The electrons which compose this space charge are given a spiral or orbital motion by a magnetic field produced by means to be described presently, and the resultant oscillation, or oscillations, about the cathode produce excitation of the anode structure at its resonant frequency or harmonics thereof. 'The function of the anode structure may be explained from a point of view that it is made up of a plurality of mutually. coupled units in each of which the inductance is provided bythe wall surface of the openings 6, and the capacitance is provided by the opposite surfaces of the associated slots 1." Assuming this point. of view, it will be observed that the operating frequency is in a large measure determined by the dimensions of the openings 6. In order to provide a magnetic field of sufficient intensity to permit the apparatus to function in its intended fashion, there are provided within the tube I tapered magnetic pole pieces [2 and I3, which may be permanently magnetized, and which are directed axially of the tube In and which :extend in close proximity to the anode structure 4.

To assure the existence of a magnetic field of desired intensity when the pole pieces I2 and I3 are permanently magnetized, these members should be constructed of a magnetizable material 1 or structure'having a high coercive force and a high energy factor. in this connection is that alloy, or group of alloys, of aluminum, nickel and cobalt. For examp1e,'one type of alloy which may be used for 1 this purpose is that described in the Mishima Patents 2,027,994 to 2,028,000. To provide a low' reluctance connection between the base extremities of the respective pole pieces I2 and I3 and the lateral wall or tube the pole pieces may be respectively seated upon relatively thick disc-like 1 members it and l5 consisting of a ferromagnetic material such as steel.

For thejpurpose of securing the pole pieces firmly to these base members, use may be made of clamping rings l6 and l'iwhichare slipped over the pole pieces and welded to the base members. Accurate spacing of. the pole pieces 12 and IS with reference to r g the anode structure may be obtained by the use 1 of spacing rings-l8 and I9 used in the manner One of the materials used flanged member 3 at the base of the entire structure.

Where it is desired to employ the magnetic pole pieces 12. and I3, either singly or jointly, as supports for one of the cooperating electrodes of the discharge device, these pole pieces may be provided, respectively, with longitudinal openings or channels 21 and 28 which are preferably of circular cross section having ends thereof which terminate in faces 29 and 30 of the pole pieces.

I provide a, rigid concentric cable structure which extends through. one of these openings or channels, such as channel 21, to Support the cathode structure in the desired spaced relation with the anode structure 4. The rigid cable construction may comprise an inner conductor 3| and an outer tubularconductor 32, both of which are preferably constructed of a refractory metal such as nickel or molybdenum, and which are maintained in the desired concentric spaced relation by means of a plurality of spaced insulators 33, 34 and 35.

I provide means for maintaining the rigid cable construction in position and which is displaced a. sufficient distance from the cathode structure, or the pole face 29, in order that it is not subjected to the heat incident to the cathode. This structure may comprise an insulator 35 and is designed to afforda long leakage path. For example, the insulator may have the configuration illustrated including a restricted portion which,

engages the outer conductor 32 and wherein the long leakage path is provided by longitudinally extending parts to have a general H-shaped cross-section. Of course, inasmuch as insulator 36 serves as a support for the. cable structure, it is apparent that the insulator closely engages the wall surface of channel 21.

As a means for supporting the cathode structure from the outer conductor 32, Iprovid a metallic electrostatic shielding member 3'! having a flanged part of a diameter equal to or less than the diameter of Opening 5, thereby shielding the insulator 36 and preventing the deposition of a conductive layer thereon which would otherwise occur incident to the evaporation of V electrons from the emissive surface of the oathode sleeve l0. Member 31 is'provided with an aperture within which an insulator 31' extends, thereby insulating and centering inner conductor 3|, Member 3'! may be welded Or soldered to the outerjconductor 32 and the entire assembly is ar ranged to minimize the heat transfer between the cathode and the concentric cable construction,

particularl outer conductor 32. One wa in which such heat transfer may be minimized i by the employment of a plurality of spaced metallic tabs 38and 39 of relatively small dimension which are made integral with .part 31 o which may be made separately and welded or otherwisejoined to the cathode sleeve l and. part 31. These tabs are of suflicient size to afiord the desiredmechanical strength of the juncture but the size and number are chosen to prevent appreciable heat transfer, from the cathode to the outer conductor 32.

Inner conductor 3| is connected to one terminal, such. as the upper terminal, of th cathode heating element II and serves to supply current thereto, the lower terminal of the cathode heating element being conductively connected to the cathode sleeve |9 which constitutes a path for the cathode heating circuit which is completed through the flanged metallic member 31 and outer conductor 32. The lower extremity of the inner conductor 3| is centered and supported by a heat resistant insulator 49 positioned at the lower end of the cathode sleeve I0.

I also provide electrostatic shielding means, such as a metallic disc 4! supported by the inner conductor 3| which extends through insulator 4B. This member serves to prevent the collection of electron current on the face of pole piece |'3.

The concentric cable construction is provided with externally accessible terminals or lead-in wires 42' and 43 which are connected, respectively, to inner conductor 3| and outer tubular conductor 32 and are, of course, arranged to aflord this connection by means of a sealing structure which may include a glass or vitreous seal 44 supported by a flanged metallic cylinder 45, the latter of which is Welded or soldered to the member 2.

In order to facilitate the evacuation of the space defined by the outer conductor 32, this element may be provided with a longitudinally extending opening or slot or slit 46. The tubular outer conductor 32 may be formed of sheet metal and the ends of the plate from which it is formed notbeing joined.

Of course, it will be appreciated that I may employ a single opening, o a series of longitudinally disposed openings, in the tubular conductor 32 which will serve equally well for the purpose c-f providing a passage, or passages, for the evacuation of gas during the exhaust process.

Energy may be extracted from the space resonant region, or regions, by any suitable output electrode means which may take the form of a loop 4? constituting an extension of an inner conducto 48 of a concentric transmission line comprising the inner conductor 48 and a concentric outer conductor 49.

In operation, upon the application of a suitable unidirectional voltage between the anode structure and the cathode, the system in its entirety will be set into oscillation, the energization of the various space resonant regions, or cavities, defined by openings 6 and slots 1 being derived from the motion of the electrons constituting the space charge between the cathode sleeve l0 and the surface or the enlarged central opening of the anode structure 4. The various space resonant regions are mutually coupled and the energy of these cavities may be supplied to an external utilization circuit through loop 41 and the concentric transmission line comprising conductors 48 and 49.

One of the principal advantages of an electric discharge device built in accordance with my invention is the ease of construction inasmuch as the coated cathode, particularly sleeve HI, may be welded to the cathode assembly as a final step in the construction thereof, thus eliminating the necessity for masking the magnetic pole pieces l2 and I3 and the other metallic partsof the structure, The outer conductor 32 of the concentric cable construction, as mentioned: above, by virtue of the slot 46 therein, permits ready escape of undesired gas from the inside of the cable during the exhaust operation; i

Fig. 3 diagrammatically illustrates a modification of my invention showing another formof a cathode structure which is supported fromithe rigid concentric cable structure, and wherein corresponding elements have been assigned like reference numerals. In the arrangement of Fig. 3,

' the cathode is supported from the outer tubular shielding member 54, preferably of disc form,

completely closes the end of cathode sleeve I and is attached thereto by means of metalli tabs 55. In this modification of my invention, the inner conductor 3| does not extend through the lower shielding member, and the lower terminal of the cathode heating element II is conductively connected to inner conductor 3| at a point nearthe' bottom of the space defined by sleeve H1.

The shielding members 5| and 54 serve to collect the electron current which would otherwise tend to travel axially along the electrodes of the discharge device to points substantially beyond the anode-cathode region.

Certain features of the electric discharge device shown inFig. 1 including the metallic containing member and the permanently magnetized magnetic field members, are disclosed and broadly claimed in the aforesaid copending patent ap plication of Elmer D. McArthur, Serial No. 447,903, filed June 22, 1942. Other features relating to certain improved aspects of the cathode support construction are disclosed and claimed in a copending application, Serial No. 465,401 of George M. White, filed concurrently herewith and which is also assigned to the assignee of this application.

While I have shown and described my invention as applied to a particular device embodying various elements diagrammatically shown, it will be obvious to those skilled in the art that changes and modifications maybe made without departing from my invention, and I, therefore, aim in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An electric discharge device comprising a plurality of cooperating enclosed electrodes including a thermionic cathod having a heating element and an anode structure surrounding said cathode, means for establishing a magnetic field comprising a magnetic pole piece substantially perpendicular to the plane of said anode structur'e, said magnetic pole piece having a channel extending longitudinally therethrough, a rigid concentric cable structure supporting said cathode and for supplying current to said heating element and comprising an inner conductor and a tubular metallic outer conductor and including a plurality of spaced insulating means therebetween, and an insulator displaced from the end *of said channel facing said anode structure and supporting said cathode structure. l.

2. An: electric discharge device Comprising a plurality of cooperating enclosed electrodes including a thermionic cathode, an anode structure surrounding said cathode, means for'establishing a magnetic field comprising a magnetic pole piece substantially perpendicular to said anode structure, said pole piece having therein a .channel extending longitudinally therethrough, a concentric cable structure supporting said cathode in spaced relation with'respect' to said anode structure and comprising an innerconductorand a tubular metallic outer conductor andha'ving a plurality of longitudinally displaced insulating means maintaining saidinner' and outer conductors in spaced relation, and an insulator dis-' in a channel extending longitudinally therethrough, and a'concentric cable structure supporting said cathode comprising an inner'conductor and a tubular metallic outer conductor including a plurality of. spaced insulating means maintaining the'conductors in spaced relation.

4. An electric discharge device comprising a plurality of cooperating enclosed electrodes including a thermionic cathode having a heating element, an anode structure. surrounding said cathode, means for establishinga magnetic field comprising a magnetic pole piece substantially perpendicular to the plane'of said anode structure, said magnetic pole piece having a channel extending longitudinally therethrough, and a concentric cable structure supporting said cathode comprising an inner conductor and a tubular metallic outer conductor and a plurality of spaced insulating means maintaining the inner and outer conductors in spaced relation... 5. -An .electric discharge device of the magnetron'type comprising a'plurality of cooperating electrodes including a cathode and an anode structure, means for establishing a'magnetic field and comprising a magnetic pole piece lying sub- 1 stantially perpendicular to the plane of said anode structure and having alongitudinal channel therethrough, an enclosure around said electrodes ductor and a tubular metallic outer conductor,

a flanged metallic member on one'side of'said V anode structure and connected to and supported by said outer conductor and having a diameter equal to or less than the diameter of the anode cathode region, said inner conductor extending through said cathode, and an electron shielding member supported by the extending-portion of said inner conductor. j 1

'7. An electric discharge device comprising a plurality of cooperating enclosed electrodes including a cylindrical thermionic cathode having therein aheating element and an anode structure substantially surrounding said cathode, a pair of magnetic pole pieces substantially perpendicular to the plane of said anode structure and positioned on opposite sides thereof, one of said pole pieces having a cylindrical channel extending longitudinally therethrough, a concentric cable structure positioned within the channel of one of said pole pieces'supporting said cathode in spaced relation with said anode structure and comprising an inner and outermetallic conductor, insulating mean displaced from the end of said one channel supporting said outer conductor,'a metallic flanged member connected to said outer conductor and said cathode and having a diameter less than that of said channel, and an electron shielding metallic member positioned between said anode structure and the other pole piece, said inner conductor extending through the cylindrical cathode and providing a support for said last mentioned member.

8. An electric discharge device comprising a plurality of cooperating enclosed electrodes including a thermionic cathode having a heating means supporting said cathode in spaced relation with respect to said anode structure and including a rigid concentric cable structurehaving an inner conductor and an outer tubular conductor,

prising a concentric cable structure supporting said cathode and for supplying current to said n e em??? a d i udin an nn r, g ne element and an anode structure substantially surrounding said cathode, means for establishing a magnetic field comprising a, magnetic pole piece substantially perpendicular to the plane of said anode structure, said magnetic pole piece having a channel extending longitudinally therethrough, a concentric cable structure supporting said cathode and for supplying current to said heating element and, including an inner conductor and a tubular outer metallic conductor, an insulator within. said channel and displaced from the end thereof facing said cathode and supportin jsaijd cable structure in said channel, and a 'metallic member connected between said cathode and said outer conductor to minimize heat transfer between said cathode and said outer conductor.

9. An electric discharge device comprising a plurality of cooperating enclosed electrode including a thermionic cathode having a heating element, an anode structure surrounding said cathode, means for establishing a magnetic field comprisinga magnetic pole piece substantially perpendicular to the plane of said anode structure, said magnetic pole piece having a channel extending longitudinally therethrough, and a concentric cable structure supporting said cathe ode comprising an inner conductor and a tubular metallic outer conductor and insulating means maintaining the inner and outer conductors in spaced relation, said outer tubular conductor being provided with an opening to facilitate evacuation of said discharge device.

10. 'An electric discharge device comprising a plurality of cooperating electrodes including a' substantially cylindrical cathode having a heating element andan anode structure substantially surroundin said cathode, a pair of magnetic pole pieces paced on opposite sides of said an,- ode structure, said pole pieces, each havingtherein a channel positioned longitudinally the pole piece, means positioning said cathode and for supplying heating current to said heating element comprising a rigid concentric cable construction including inner and outer conductors extending through the channel of one of said pole pieces and having externally accessible terminals, means connecting the outer conductor of said cable to one end of said cathode, and means positioned in said channel and engaging said outer conductor to position said cable with respect to said anode structure.

11. An electric discharge device comprising a plurality of cooperating electrodes including an elongated cathode and an anode structure surrounding said cathode, a pair of magnetic pole pieces spaced on opposite sides of said anode structure, said pole pieces each having therein a channel positioned longitudinally of the pole piece, and means positioning said cathode comprising a concentric cable construction attached to said cathode and extending through the channel of one of said pole pieces and an insulator in said channel and engaging said cable to center said cable, said insulator having a creepage path from said cable to the wall of said channel substantially greater than the shortest distance between said cable and said wall.

12. An electric discharge device comprising a plurality of enclosed cooperating electrodes including a thermionic cathode including a heating element and an anode structure surrounding said cathode, a pair of magnetic pole pieces spaced on opposite sides of said anode structure and each having therein a channel of circular cross section positioned longitudinally of the pole piece, means supporting said cathode and for supplying current to said heating element comprising a rigid concentric cable construction including an inner and outer conductor extending through the channel of one of said pole pieces, and an insulator fitted in the channel of said one pole piece and engaging said outer conductor to center said cable and thereby to center said cathode with respect to said anode.

13. An electric discharge device comprising a plurality of cooperating electrodes including a cylindrical thermionic cathode and an anode structure of annular form having a circular center opening Within which said cathode is located, a pair of magnetic pole pieces spaced on opposite sides of said anode structure, said pole pieces each having therein a channel positioned longitudinally of the pole piece, means positioning said cathode comprising a concentric cable construction extending through the channel of one of said pole pieces and comprising an inner conductor and a concentric outer conductor and insulating means therebetween, an insulator positioned in the channel of said one pole piece within the vicinity of the pole face supporting and centering said cable, a cathode heating element surrounded by said cylindrical cathode and having one terminal electrically connected to said inner conductor, and a metallic member connected to the other terminal of said cathode heating element and said outer conductor and spaced between said cathode and said insulator to prevent the condensation of conductive material on said insulator.

14. An electric discharge device comprising a plurality of cooperating electrodes including a thermionic cathode having an emissive surface and an anode structure surrounding said cathode, a pair of magnetic pole pieces spaced on opposite sides of said anode structure, said pole pieces each having therein a channel positioned longitudinally of the pole piece, means positioning said cathode comprising a concentric cable construction extending through the channel of one of said pole pieces and attached to said cathode, an insulator positioned in the channel of one of said pole pieces within the vicinity of the pole face, and shielding means positioned between said cathode and said insulator, to prevent the deposition of conductive material on said insulator.

15. An electric discharge device comprising a plurality of cooperating electrodes including a thermionic cathode having an emissive surface and an anode structure surrounding said cathode, a pair of magnetic pole pieces spaced on opposite sides of said anode'structure, said pole pieces each having therein a channel positioned longitudinally of the pole piece, means positioning said cathode comprising a concentric cable construction extending through the channel of one of said pole pieces and attached to said cathode, an insulator positioned in the channel of one of said pole pieces Within the vicinity of the pole face, and conductive means constituting a part of said cathode shielding said insulator to prevent the deposition of conductive material thereon.

RALPH J. BONDLEY. 

